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Can killifish fry kill each other?

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I have bought some killifish eggs online. I ended up with 5 fry that seemed healthy.
I had 2 bigger ones of about 1 cm long from head to tail and 3 smaller ones.
A few days ago I did notice the two big ones fighting. I didn't make much attention as I noticed that they kind of were avoiding each other after that.
Yesterday I have found one of the big fry dead. The others seem to be as healthy and active as before, and they are eating well, so it can't be the water.
Could it be possible that it was killed by the other big fry, or maybe stress got to him?

Yes they can. They come from a life cycle where they are in a survival of the fittest scenario. It is possible that they harass each other and that they create a dominant structure as they are not a schooling fish.

Just like taking 100 baby humans, each have different growth rates. Every fish is a different life and you will have runts, mishapen fish, etc... Its possible you get females being smaller but in my exp, my killi females were always wide chested where the males were more slender headed. Obviously once they start coloring you will know for sure.

Thanks, that's good information. I didn't know what to expect when I bought the eggs, I needed some fishes for the top of the tank, and I thought it would be interesting to grow them from eggs. I was interested in killifishes for a long while but could never find them in shops where I live.